Shunt barrier in pulse oximeter sensor

ABSTRACT

A pulse oximeter sensor having an emitter(s) and a detector, with a layer having a first portion of the emitter and a second portion of layer over the detector is provided. A barrier is included between the first and second portions of the overlying layer to substantially block radiation of the wavelengths emitted by the emitter(s). Preferably, the barrier reduces the radiation shunted to less than 10% of the radiation detected, and more preferably to less than 1% of the radiation detected.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional of U.S. Application Ser. No.09/750,670, filed Dec. 28, 2000, now U.S. Pat. No. 6,430,423, which is adivisional of U.S. Application Ser. No. 09/085,698, filed May 27, 1998,now U.S. Pat. No. 6,173,196, which is a continuation of U.S. ApplicationSer. No. 08/611,151, filed Mar. 5, 1996, now U.S. Pat. No. 5,797,841,the disclosures of which are incorporated by reference.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH OR DEVELOPMENT

Not Applicable

REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAMLISTING APPENDIX SUBMITTED ON A COMPACT DISK

Not Applicable

BACKGROUND OF THE INVENTION

The present invention relates to pulse oximeter sensors, and inparticular to methods and apparatus for preventing the shunting of lightbetween the emitter and detector without passing through blood-perfusedtissue.

Pulse oximetry is typically used to measure various blood flowcharacteristics including, but not limited to, the blood-oxygensaturation of hemoglobin in arterial blood, the volume of individualblood pulsations supplying the tissue, and the rate of blood pulsationscorresponding to each heartbeat of a patient. Measurement of thesecharacteristics has been accomplished by use of a non-invasive sensorwhich scatters light through a portion of the patient's tissue whereblood perfuses the tissue, and photoelectrically senses the absorptionof light in such tissue. The amount of light absorbed is then used tocalculate the amount of blood constituent being measured.

The light scattered through the tissue is selected to be of one or morewavelengths that are absorbed by the blood in an amount representativeof the amount of the blood constituent present in the blood. The amountof transmitted light scattered through the tissue will vary inaccordance with the changing amount of blood constituent in the tissueand the related light absorption. For measuring blood oxygen level, suchsensors have typically been provided with a light source that is adaptedto generate light of at least two different wavelengths, and withphotodetectors sensitive to both of those wavelengths, in accordancewith known techniques for measuring blood oxygen saturation.

Known non-invasive sensors include devices that are secured to a portionof the body, such as a finger, an ear or the scalp. In animals andhumans, the tissue of these body portions is perfused with blood and thetissue surface is readily accessible to the sensor.

One problem with such sensors is the detection of ambient light by thephotodetector, which can distort the signal. Another problem is theshunting of light directly from the photo-emitter to the photodetectorwithout passing through blood-perfused tissue. FIG. 1 illustrates twodifferent types of light shunting that can interfere with properdetection of oxygen saturation levels. As shown in FIG. 1, a sensor 10is wrapped around the tip of a finger 12. The sensor includes a lightemitter 14 and a light detector 16. Preferably, light from emitter 14passes through finger 12 to be detected at detector 16, except foramounts absorbed by the blood-perfused tissue.

A first type of shunting, referred to as type 1 shunting, is shuntinginside the sensor body as illustrated by light path 18, shown as a wavyline in FIG. 1. Light shunts through the sensor body with the sensorbody acting like a light guide or light pipe, directing light from theemitter to the detector.

A second type of shunting, referred to as type 2 shunting, isillustrated by line 20 in FIG. 1. This type of light exits the sensoritself, but reaches the detector without passing through the finger. Inthe embodiment shown, the light can go around the side of the finger,perhaps by being piped by the sensor body to the edges of the sensor andthen jumping through the air gap between the two edges which are wrappedaround the side of the finger.

The problem of light shunting can be exacerbated by layers placed overthe emitter and detector. Often, it is desirable not to have the emitterand detector in direct contact with the patient's skin because motionartifacts can be reduced by placing a thin layer of adhesive betweenthese components and the skin. Thus, the emitter and detector aretypically covered with a clear layer which isolates them from thepatient, but allows light to transmit through. The feature of allowinglight to transmit through the layer also provides the capability for theclear layer to provide a wave guide effect to shunt light around thefinger to the detector.

Such layers covering the emitter and detector can be originally includedin the sensor, or can be added during a reinforcing or modifyingprocedure, or during a remanufacture of the sensor. In a remanufactureof a sensor, a sensor which has been used may have its outer, adhesivetransparent layer removed. Such a layer is shown in FIG. 2 as atransparent layer 22 over a sensor 10. Layer 22 is an adhesive,transparent layer placed over a substrate layer 24, upon which emitter14 and detector 16 are mounted, along with any other associatedelectronics. Layer 22 thus serves both to protect the emitter anddetector from the patient, and to adhere the sensor to the patient.During remanufacture, this layer can be stripped off, and a new layerplaced thereon.

Alternately, layer 22 may be left in place. Such a sensor, with anadhesive outer layer, may be a disposable sensor, since it would not bedesirable to have the same adhesive used from one patient to another,and an adhesive is difficult to clean without removing the adhesive.Accordingly, a modification of such a sensor may involve laminatingsensor 10 to cover over the adhesive, by adding an additional laminationlayer 23 (shown partially broken away) over layer 22. The laminationlayer is itself another layer for shunting light undesirably from theemitter to the detector. Once laminated, in one method, the sensor isthen placed into a pocket 26 of a sheath 32. Sheath 32 includes atransparent cover 28 on an adhesive layer 30. Layer 30 is adhesive forattaching to a patient. Layer 28 may also optionally be adhesive-coatedon the side which faces the patient. Such a modified sensor can bereused by using a new sheath 32. Transparent layer 28 forms yet anothershunting path for the light.

A commercially available remanufactured sensor, similar in design to thesensor of FIG. 2, is available from Medical Taping Systems, Inc. Anotherexample of a sheath or sleeve for a sensor is shown in U.S. Pat. No.4,090,410, assigned to Datascope Investment Corp.

In addition, when a sheath such as 32 is folded over the end of apatient's finger, it has a tendency to form wrinkles, with small airgaps in-between the wrinkled portions. The air gaps can actuallyexacerbate the shunting problem, with light jumping more easily throughthe air gaps from one portion of the transparent layer to another.

Other types of sensors have not used a solid transparent layer 22 asshown in FIG. 2. For instance, the Nellcor Puritan Bennett R-15Oxisensor® and N-25 Neonatal/Adult Oxisensor products use awhite-colored substrate with separate transparent strips placed over theemitter and detector (such as strips 11 and 13 illustrated in FIG. 1).The transparent strips are adhesive for adhering to the patient. Sincetwo strips are used, an air gap (gap 15 in FIG. 1) occurs between thetransparent layers. As noted above, light can jump such an air gap, andthus a gap by itself may not eliminate all shunting problems. The use ofa dark-colored substrate may reduce the amount of shunting, if theselected color is opaque to the wavelengths of interest from theemitter, 650 nm red and 905 nm infrared in a typical implementation.However, the white substrate typically used in the R-15 and N-25 sensorsis substantially translucent and thus has limited light blockingqualities.

It has been found that shunted light can significantly affect theaccuracy of oxygen saturation readings using a pulse oximeter.Accordingly, there is a need to develop a barrier to such light toimprove the accuracy of pulse oximeter sensors.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a sensor having an emitter(s) and adetector, with a layer having a first portion over the emitter and asecond portion over the detector. A shunt barrier is included betweenthe first and second portions of the overlying layer to substantiallyblock transmission of radiation of the wavelengths emitted by theemitter(s). Preferably, the shunt barrier reduces the radiation shuntedto less than 10% of the total radiation detected, and more preferably toless than 1% of the total radiation detected, when the sensor is used onpatients having the most opaque tissue of all patients in the targetpopulation.

In particular for a remanufactured or reinforced or modified sensor, thebarrier is added in at least one, and more preferably in all, of theextra layers added or replaced during the remanufacturing, reinforcingor modifying process. The barrier of the present invention may take anumber of specific forms. In one embodiment, a woven or fiber materialis included between the emitter and detector. In another embodiment, thelayer in-between the emitter and detector is pigmented with a colorwhich is substantially opaque for the wavelengths of interest, while theportion above the emitter and detector is substantially transparent. Inanother embodiment, the entire layer is partially opaque, but is thinenough so that light transmitted through is able to penetrate thepartially opaque layer, while light traveling the length of the layerwould have a greater distance to travel and would be substantiallyabsorbed.

Another shunt barrier is the insertion of perforations in the layerbetween the emitter and detector. The perforations may provide air gaps,which still will shunt some light, or may be filled with other materialor have the insides of the perforations colored with an opaque color.

In another embodiment, the layer between the emitter and detector ismade very thin, such as by embossing, welding or heat sealing. Thethinness of the material will limit its effectiveness as a light pipe inthe wavelengths of interest, red and infrared.

In another embodiment, a deformable, opaque material, such as foam, isincluded between the emitter and detector, to be compressed uponapplication to a finger or other body part and fill any gap that mightotherwise form through wrinkles or otherwise upon application of thesensor.

In another embodiment, an adhesive is applied in a gap between twolayers over the emitter and detector, to cause an underlying layer tocome in contact with the patient, thus filling the air gap andpreventing shunting along that path.

While most of the illustrative examples given in this specification areshown as sensors adapted to be wrapped onto a digit, so that light istransmitted through the digit, it will be clear to those skilled in theart that the design principles illustrated may be applied to any“transmittance” or “reflectance” sensors for pulse oximetry. A typicalreflectance sensor is the Nellcor Puritan Bennett RS-10.

For a further understanding of the nature and advantages of theinvention, reference should be made to the following description takenin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating the shunting that occurs upon theplacement of a sensor over a finger;

FIG. 2 is a diagram of a sensor being placed within a reusable sheath ina sensor modification operation;

FIGS. 3A and 3B are diagrams of one embodiment of a shunt barriershowing an opaque film abutting both an air gap and another layer;

FIG. 4 is a diagram of a sensor with a woven or fiber material for ashunt barrier;

FIG. 5 is a diagram of a sensor with a partially opaque material for ashunt barrier, with a trade-off between transmission intensity andpreventing shunting;

FIG. 6 is a diagram of a sensor using perforations as a shunt barrier;

FIG. 7 is a diagram of a sensor with a thinned layer between emitter anddetector as a shunt barrier;

FIG. 8 is a diagram of a sensor using differential coloring as a shuntbarrier;

FIG. 9 is a diagram of a sensor using an adhesive in a gap betweenlayers over the emitter and detector for a shunt barrier;

FIG. 10 is a diagram of a sensor using a foam pad between the emitterand detector as a shunt barrier;

FIG. 11 is a diagram of a sensor using a solid barrier as a shuntbarrier;

FIG. 12 is a diagram of a sensor showing the use of overlapping layersas a shunt barrier;

FIG. 13 is a diagram of a sensor using a barrier of metal traces forminga tortuous path between emitter and detector as a shunt barrier; and

FIG. 14 is a diagram of a sheath incorporating a colored ring around theemitter and detector windows as a shunt barrier.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 3A and 3B illustrate the use of an opaque film adjacent anotherlayer or an air gap to absorb shunting light. FIG. 3A shows the opaquefilm 34, before assembly being placed over layers 36, 36′ separated byan air gap 38. Layers 36, 36′ may be mounted on a common substrate (notshown). Holes 40 and 42 are shown for the emitter and detector.Alternately, these can be windows or simply a solid portion of atransparent layer. FIG. 3B shows the assembled lower layer and opaquefilm layer 34. As light attempts to shunt from emitter area 40 todetector area 42, either passing through the air gap 38 or throughlayers 36 and 36′, it will bounce back and forth between the boundariesof the layer and through the air gap. Some of the light that wouldnormally hit the top end of layer 36 or 36′ and bounce back into themiddle of the layer, will instead pass into and be absorbed by opaquelayer 34, which is tightly coupled to the layers 36 and 36′.

FIG. 4 illustrates the use of a woven or fiber material 44 on layers 36and 36′, and filling the air gap 38 of FIG. 3A. Fibers in the materialwill absorb light, thus attenuating light attempting to shunt fromemitter area 40 to detector area 42. An additional cover layer 46 may beplaced over the assembly, and which will need to be at least partiallytransparent for light to escape and be detected. Layer 46 can functionas another shunting layer. By abutting up against the woven or fibermaterial 44, light will be absorbed out of that layer in the same manneras the opaque film 34 of FIGS. 3A and B. Alternately, the fiber andwoven material can be inserted into layer 46 between the emitter anddetector.

FIG. 5 shows an alternate embodiment in which a layer 50 is used with anemitter 52 placed on top of it. Alternately, layer 50 could have holes54 and 56 over the emitter and detector, with the emitter 52 beingplaced through hole 54 onto an underlying layer. A partially opaquelayer 58 is placed above emitter 52 in the embodiment shown. Layer 58may extend a portion of the way or all of the way over to where thedetector is. The opacity of layer 58 is chosen in conjunction with itsthickness to allow transmission of substantially all of the light fromemitter 52 through the layer, while substantially reducing the amount oflight shunted in a path transverse through the layer from the emitter tothe detector. Layer 58 preferably attenuates the shunted light so thatit is less than 10%, and more preferably less than 1% of the total lightreceived by the detector. Additionally, of the light detected by thedetector and converted into electrical signal, the portion of theelectrical signal due to shunted light is preferably less than 10% andmore preferably less than 1% of the signal value.

The layer may be made substantially opaque through coloring. One suchcolor would be a gray created by suspension of carbon black particles inthe base material of the layer. This would be substantially opaque toboth red and infrared.

FIG. 6 shows another embodiment of the invention in which a layer 60over an emitter 62 and detector 64 has a series of perforations 66.These perforations block the light path and scatter the light attemptingto shunt between the emitter 62 and detector 64 through layer 60.Although light tends to jump air gaps, by providing multiple air gaps indifferent orientations, the light can be somewhat effectively scattered.Alternately, the perforations could be filled with a colored fillingmaterial or putty to block the light that might otherwise jump the airgaps, or could have the inside walls of the perforations colored.Alternately, embossing (or other variations in thickness) could be usedrather than perforations.

FIG. 7 illustrates a layer 70 having an emitter 72 and detector 74,covered by another layer 76. Layer 76 may be partially transparent forlight to exit from emitter 72 and re-enter to detector 74. Layer 76 hasa thinned portion 78, and layer 70 has a corresponding thinned portion79. These portions make the layers thin in that area, thus limiting theamount of light that may be shunted. The layer could be made thin by anumber of techniques, such as embossing, welding or heat sealing. Thewidth of the thinned area could be varied, and the shape could be variedas desired. For instance, the thinned area could extend around the sidesof the emitter and detector, to prevent shunting of light from the edgesof the layers when they are wrapped around a finger.

The thinness of the layer contributes to absorption of the light becauselight which is traveling in a thin layer will more often bounce off thelayer boundaries than it would in a thick layer. This provides morechances to escape the layer and be lost or absorbed in an adjoininglayer with absorption characteristics.

The thickness is preferably less than 0.25 mm and more preferably nomore than 0.025 mm. The length of the thin section is preferably greaterthan 1 mm and more preferably greater than 3 mm.

The thin layer approach could be applied to a re-manufacture or othermodification of a sensor which involves adding a layer over the emitterand detector. The entire layer could be made thin, preferably less than0.25 mm, more preferably no more than 0.025 mm, in order to limit itsshunting effect.

FIG. 8 shows a sensor having a layer 80 for an emitter 81 and a detector82, having transparent windows 83 and 84, respectively. A substratelayer 85 supports the emitter and detector, with light being transmittedthrough transparent window 83 and received through window 84. In oneembodiment, the entire layer 80 is opaque, leaving transparent portions83 and 84. Alternately, the entire layer 80 may be transparent, or ofone color with the windows of another or transparent. In addition, aportion 86 of layer 80 between the emitter and detector may be colored asubstantially opaque color to prevent the shunting of light of thewavelengths of interest. In alternate embodiments, portion 86 may be ofdifferent shapes, and may partially or totally enclose the windows forthe emitter and detector.

FIG. 9 shows another embodiment of a sensor according to the presentinvention mounted on a finger 90. Two portions of a first layer, 91, 91′have the emitter 92 and detector 93, respectively, attached to them. Abreak between layers 91 and 91′ is provided in between the emitter anddetector, which will be at the tip of finger 90. Normally, this gapwould provide an air gap through which light can be shunted between theemitter and detector across the top of the finger. However, by using abacking layer 94, with an adhesive in the portion between layers 91 and91′, this layer can stick to the tip of finger 90, removing the air gapand thus substantially preventing shunting between the layers.

An alternate embodiment is shown in FIG. 10, with the finger 100 havinga sensor with layers 91 and 91′ and emitter 92 and detector 93 as inFIG. 9. Here, however, a separate layer 94 is provided with a foam orother resilient or compressible pad 96 mounted on layer 94 betweenlayers 91 and 91′. This material will compress against the tip of thefinger, thus also blocking the air gap and preventing the shunting oflight if the material is made of a substantially opaque material, suchas a color that is substantially opaque to the wavelengths of interest(e.g., red and infrared), or is made of woven material or other materialopaque to the light.

FIG. 11 is another embodiment of the present invention showing a layer110 having an emitter 112 and a detector 114 mounted thereon. Acovering, transparent layer 116 provides a covering and a window for thetransmission and detection of light. Shunting of light is prevented bycrimping the layers with a metal or other crimp 118, 120. The metal orother material is substantially opaque to the shunted light of thewavelengths of interest, and completely penetrates the layer, orsubstantially penetrates the layer.

FIG. 12 shows an alternate embodiment in which a layer 121 has anemitter 122 and a detector 124 (both shown in phantom) mounted thereon.Over the emitter area is a first transparent layer 126, with a secondtransparent layer 128 over the detector 124. As can be seen, the twolayers are overlapping, with the end 129 of layer 128 being on top oflayer 126. Thus, instead of an air gap, any shunted light from layer 128is deflected to be above layer 126, and vice versa. Alternately, sincethe light will originate from the emitter, it may be more preferable tohave the layer overlaying the emitter be on top of the layer overlayingthe detector. In the overlapping portion, a radiation blocking layer maybe included, such as a colored adhesive.

FIG. 13 shows an alternate embodiment of the present invention in whicha flexible circuit is printed onto a layer 130. As shown, emitter 132and detector 134 are mounted on the flexible layer 130. A covering layer133 is provided. Layers 130 and 133 may be partially or substantiallyopaque to prevent the shunting of light. In between the layers, metaltraces 136 and 138 can be used to block the shunting of light. Insteadof making these traces run lengthwise, leaving a clear path between theemitter and detector, they instead follow a tortuous path. This tortuouspath not only goes lengthwise, but also goes across the width of thelayer 130, thus providing a barrier to block shunting the light betweenthe emitter and detector.

FIG. 14 shows another embodiment of the present invention for modifyinga sheath such as sheath 32 of FIG. 2. FIG. 14 shows a sheath 140 havinga first, adhesive layer 142, and a second layer 144 being transparentand forming a pocket for the insertion of a sensor. Layer 144 has opaquecolored rings 146 and 148 surrounding windows 147 and 149, respectively.These windows allow the transmission of light to and from the emitterand detector, while the opaque rings prevent the shunting of lightthrough transparent layer 144. Alternately, more or less of thetransparent layer 144 could be colored with an opaque color to preventthe shunting of light.

Alternately, in the embodiment of FIG. 14, windows 147 and 149 could beone color, while areas 146 and 148, which may extend over the rest ofthe layer 144, could be of a second color. The second color would bechosen to prevent shunting, while the first color would be chosen toallow the transmission of light while also being of a color which iscompatible with the calibration data for an oximeter sensor. If thecolor over the emitter and detector is not chosen properly, it mayinterfere with the choice of a proper calibration curve in the oximetersensor for the particular wavelength of the emitter being used.Typically, LEDs of slightly varying wavelengths are used, with a codingresistor indicating the exact wavelength. The coding resistor is used tochoose a particular calibration curve of coefficients in the oximetersensor. Thus, by using a differentially-colored sheath or reinforcinglaminate or other layer, with the layer near the emitter and detectorchosen to be white, clear or other color which does not interfere withthe calibration, shunting can be prevented while allowing the sensor tobe used without affecting its standard calibration. Preferably, theregions over the emitter and detector have a radius extending at least 2mm. beyond the borders of the emitter and detector, and preferably atleast 5 mm beyond the borders of the emitter and detector.

Any of the shunt barriers described above could be incorporated intolayer 144 of sheath 140 of FIG. 14. Alternately, or in addition, theshunt barriers could be incorporated into a lamination or other layerplaced over a sensor in a modifying process. Such a modifying processmay, for instance, place a non-adhesive layer over an adhesive layer toconvert a disposable sensor into a reusable sensor. The shunt barriersdescribed above may also be in an original layer in a sensor, or in areplacement layer added in a remanufacturing process for recyclingdisposable sensors.

As will be understood by those of skill in the art, the presentinvention may be embodied in other specific forms without departing fromthe spirit or essential characteristics thereof. Accordingly, theforegoing description is intended to be illustrative, but not limiting,of the scope of the invention which is set forth in the followingclaims.

What is claimed is:
 1. A sensor comprising: at least one emitter; adetector; a covering layer having a first portion over the emitter and asecond portion over the detector; a shunt barrier positioned betweensaid first and second portions of said covering layer to substantiallyblock radiation of the wavelengths emitted by said emitter, such thatless than 10% of the radiation detected by said detector is shuntedradiation, said shunt barrier extending across a width of said sensorbeing entirely contained between any emitter, including said at leastone emitter, and said detector, wherein said shunt barrier comprises acolored layer portion.
 2. The sensor of claim 1 wherein said coloredlayer portion is white.
 3. A sensor comprising: at least one emitter; adetector; a covering layer having a first portion over the emitter and asecond portion over the detector; a shunt barrier positioned betweensaid first and second portions of said covering layer to substantiallyblock radiation of the wavelengths emitted by said emitter, such thatless than 10% of the radiation detected by said detector is shuntedradiation, said shunt barrier extending across a width of said sensorbeing entirely contained between any emitter, including said at leastone emitter, and said detector, wherein said shunt barrier comprises acolored layer portion; wherein said sensor is a pulse oximeter sensorfor use with a pulse oximeter having calibration curves for wavelengthsof said emitter, said first and second portions have a color compatiblewith said calibration curves in an area of said first and secondportions within a radius extending at least 2 mm beyond the borders ofsaid emitter or said detector.
 4. The sensor of claim 3 wherein saidfirst and second portions with a color compatible area are within aradius of 10 mm beyond the borders of said emitter and said detector.